China
Africa
Explore chapters and articles related to this topic
Hydropower and Marine Energy
Published in Radian Belu, Fundamentals and Source Characteristics of Renewable Energy Systems, 2019
The tides are cyclic or periodic variations in the level of seas and oceans, representing the planetary manifestation of the potential and kinetic energy fluxes present in the Earth-Moon–Sun system. This results in some regions of the world possessing substantially higher local tidal variation than others. Tidal energy is energy generated from tidal movements, containing both potential energy, related to the vertical fluctuations in sea level, and kinetic energy, related to the horizontal motion of the water column. Tidal periodicity varies according to the lunar and solar gravitational effects, respective movements of the Moon and Sun, and other geographical peculiarities. The mean interval between conjunctions of the Sun and Moon has a cycle of 29.53 days, which is known as Synodic month or lunation. There are three different types of tidal phenomena at different Earth locations. Semidiurnal tides with monthly variation has a period of 12 hours 25 minutes, due to the Earth rotation relative to both Sun and Moon, consequently the tidal phenomenon occurs twice every 24 hours 50 minutes 28 seconds, each landmass is exposed to two high tides and two low tides during each period of rotation. Tide amplitude varies according to the lunar month, with higher tidal range at full Moon and new Moon, when Sun and Moon are aligned. Neap tides occur during half-moon as the resultant gravitational pull is at its minimum. However, one of the tides has greater range than the other, having a higher high and a lower low, therefore, a greater tidal flow while water is coming in and going out during the period between high and low level. Furthermore, the tidal output peaks and troughs four times a day as the tide comes in and out twice daily. Diurnal tides with monthly variation are found in China Sea and Tahiti, having the tidal period is of 24 hours 50 minutes 28 seconds. During each Earth rotation, a point of the Earth surface pass through different parts of the equilibrium tide envelope and therefore experience a diurnal variation in tide levels. Mixed tides combine the characteristics of diurnal and semidiurnal tides. Moreover, they can also display monthly and bimonthly variation. They are found in the Mediterranean Sea. Moreover, there are several periodic phenomena that are affecting the tidal behavior.
Cyclic tidalites and seismites at a submarine hydrothermal system for a 2450 Ma banded iron formation, Hamersley Basin, Western Australia
Published in Australian Journal of Earth Sciences, 2023
Taking 28 ± 2 semidiurnal microbands per fortnightly cycle for the Weeli Wolli cycle period implies 28 ± 2 lunar days, or 29 ± 2 solar days, per lunar month at 2450 Ma. There are currently 29.53 solar days per lunar month. The plot of Lambeck (1980, figure 11.5) gives a projected period of 30.5–30.7 solar days per lunar month for the early Paleoproterozoic (2500–2400 Ma) for an average equivalent phase lag angle of 3° (the angle between the Earth–Moon axis and Earth’s tidal bulge), which accords with the late Cryogenian Elatina–Reynella paleotidal data (Williams, 1989, 2000). The Weeli Wolli datum is broadly consistent with that projected period.